Explosive projectiles are well known in the art but mainly for large weapons. The present invention pertains to projectiles which are provided in cartridge form and are particularly suitable for use in standard 12 bore shotguns. However, the projectiles according to the present invention are equally applicable to shotguns of greater or smaller bores.
Gawlick et al U.S. Pat. No. 3,576,165 and German DE-3033061 disclose a projectile having a safety device including a locking pin, one end of which is inserted into the projectile perpendicular to the projectile axis, which prevents premature detonation. The outer head of the pin is flush with the outer surface of the projectile, so that, in use, the pin can contact the barrel of the weapon from which it is fired. Since the pin is outwardly spring-biased, it is urged radially outwardly and hence ejects after leaving the barrel to arm the warhead. However, such projectiles contact an intermediate objects prior to reaching the target, the active charge may be prematurely initiated. If this occurs too soon after the operator has fired the projectile, the operator could himself be in danger. Although the Gawlick patent discloses that the safety pin is ejected a finite period of time after the projectile leaves the barrel, it does not disclose a method for ensuring that the safety pin is not ejected prematurely. This problem has been addressed in U.S. Pat. No. 4,697,524 (EPA-0-147932). The solution proposed therein is to provide a locking pin which is ejected by gas pressure alone. The inherent complexity of this solution leads to high costs and munitions failure in use.
The problem of premature detonation of the warhead is especially severe for non-self-propelled projectiles which have fins angled with respect to the axis of the projectile so as to impart spin. This is so because upon exiting the barrel, the wind resistance of the fins causes a rapid deceleration of the projectile which tends to drive the firing pin into the initiator if the safety pin is ejected too soon.
Leonard et al. U.S. Pat. No. 3,820,463 discloses a shotgun grenade comprising a warhead portion interfitted with a grenade casing provided at its rear end with a plurality of circumferential ribs for stability in flight. This device, although available since 1974, has not been in use for a number of reasons. In the first place, the safety pin is a shear pin adapted to fracture on impact. Such shear pins also fracture if the grenade is inadvertently dropped with serious consequences for the user. Shear pins can also remain intact if the grenade is fired into water, snow, soft mud, etc. leading to a failure of the round to detonate in use. Moreover, it is important in this approach that the nose portion be rifled to impart spin. However, since shotgun barrels are rarely rifled, the actual spin imparted is usually minimal and hence accuracy is impaired. Finally it should be noted that the actual grenade is only 3.6 cm long, hence the amount of collateral damage achievable by use of this device is relatively small.
Kopsch U.S. Pat. No. 4,434,718 and Abbott U.S. Pat. No. 3,650,213 each provide a finned projectile for firing from a 12 bore shotgun. In these devices the projectile is provided with fixed fins to impart spin. Unfortunately, the effect of the use of fixed fins is to reduce the size of the payload (throw-weight). Further, in neither of these documents is a separate arming device or safety device discussed.
Russell-French U.S. Pat. No. 3,177,809 discloses rocket assisted artillery rounds provided with a cartridge case extending only over a portion of the folded down fins so that, when the round is fired from the barrel of an artillery piece, the fins are urged by a spring to deploy to their radially outward positions, thereby stabilizing the rocket propelled round during its flight. However, the use of folded down fins has not been described with reference to ammunition without its own means of propulsion.
Jones U.S. Pat. No. 2,755,738 discloses safety fuses for rockets which provide locking elements which lock the firing mechanism of a missile until it leaves its barrel, whereupon the elements disengage under radial spring pressure to release a firing pin. A similar device is to be found in Gawlick et al. U.S. Pat. No. 3,638,571, wherein a recoil-less mortar practice round is described. Both the Gawlick and Jones patents relate to missiles with their own propellant system. Self-propelled missiles have a high mass and are driven by self-generated propellant gas to accelerate from the barrel with only marginal deceleration upon exiting from the muzzle.